U.S. patent number 4,469,554 [Application Number 06/482,213] was granted by the patent office on 1984-09-04 for etch procedure for optical fibers.
This patent grant is currently assigned to AT&T Bell Laboratories. Invention is credited to Dennis R. Turner.
United States Patent |
4,469,554 |
Turner |
September 4, 1984 |
Etch procedure for optical fibers
Abstract
A process is described for etching a tapered point on a
cylindrically symmetric body using an inert liquid layer on top of
the etching solution. The process is extremely useful for etching
tapered points on optical fibers prior to melt-back to form a small
lens to couple light from laser to optical fiber. The process
produces excellent tapered points rapidly and reproducibly with a
minimum of operator attention and without etch marks above the
taper.
Inventors: |
Turner; Dennis R. (Chatham
Township, Morris County, NJ) |
Assignee: |
AT&T Bell Laboratories
(Murray Hill, NJ)
|
Family
ID: |
23915176 |
Appl.
No.: |
06/482,213 |
Filed: |
April 5, 1983 |
Current U.S.
Class: |
216/97; 216/11;
216/90; 216/99; 252/79.3; 252/79.4 |
Current CPC
Class: |
C03C
15/00 (20130101); G02B 6/4202 (20130101) |
Current International
Class: |
C03C
15/00 (20060101); G02B 6/42 (20060101); C03C
025/06 (); C09K 013/08 (); C09K 013/06 () |
Field of
Search: |
;204/129.55,228,129.75
;156/626,627,637,663,659.1 ;252/79.3,79.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Crow, J. D. and Harper, J. S., IBM Technical Discl., vol. 20, #3,
Aug. 1977, "Fabrication of Lenses on Tips of Fibers". .
J. S. Sconce, Chlorine, Krieger Publishing Co., Huntington, N.Y.,
1972, pp. 82, 95, 99..
|
Primary Examiner: Valentine; Donald R.
Attorney, Agent or Firm: Nilsen; Walter G.
Claims
What is claimed is:
1. Process comprising at least partially immersing a cylindrically
symmetric body in first liquid in order to etch the cylindrically
symmetric body characterized in that a second liquid is located on
top of the first liquid, said second liquid being substantially
non-etching and substantially immiscible in the first liquid and
the cylindrically symmetric body is a glass optical fiber
consisting of at least 80 weight percent silicon dioxide.
2. The process of claim 1 in which the second liquid has density
less than the first liquid.
3. The process of claim 2 in which the second liquid consists
essentially of at least one substance selected from the group
consisting of sunflower seed oil, mineral oil, motor oil, heavy
gear oil, synthetic motor oil, castor oil, corn oil, linseed oil,
and whale oil.
4. The process of claim 1 in which the cylindrically symmetric body
is etched to a tapered point.
5. The process of claim 1 in which the glass optical fiber consists
of at least 90 weight percent silicon dioxide.
6. The process of claim 5 in which the glass optical fiber consists
of at least 95 weight percent silicon dioxide.
7. The process of claim 1 in which the first liquid is aqueous
hydrofluoric acid.
8. The process of claim 7 in which the concentration of the aqueous
hydrofluoric acid is between 35 weight percent and near 100 weight
percent.
9. The process of claim 8 in which the concentration of the aqueous
hydrofluoric acid is about 49 weight percent.
10. Process for producing an optical fiber with a lens by melting
back a tapered point to form the lens in which the tapered point is
made by at least partially immersing the optical fiber in a first
liquid in order to etch the optical fiber characterized in that a
second liquid is located on top of the first liquid, said second
liquid being substantially non-etching and substantially immiscible
in the first liquid.
Description
TECHNICAL FIELD
The invention is an etching procedure for shaping various materials
including glass fibers and particularly including the ends of
fibers used for optical communications.
BACKGROUND OF THE INVENTION
Various silica glass devices and articles have become of intense
interest in recent years for a variety of reasons generally
associated with the development of optical devices and the
development of optical communication systems. Particularly
important has been the development of various processes for
producing silica-glass devices of high quality for use in optical
devices and optical communication devices.
Much attention and effort has been applied to the manufacture of
optical fibers for use in optical communication systems. Here,
exact standards are required to insure low-loss and low-distortion
transmission of optical signals down the optical fiber so as to
achieve maximum bandwidth and maximum distance between repeater
stations. Often in the manufacture of optical devices involving
optical glasses (including optical fibers) various shaping
operations involving etching are required.
A particularly difficult problem involves coupling radiation in and
out of the ends of the optical fibers. This often involves shaping
a lens type structure at the end of the fiber to increase the
coupling of light between device (e.g., source or detector) and
optical fiber. For example, with an optical source such as a laser,
increased efficiency is obtained by shaping a small lens at the end
of the optical fiber to increase the coupling of laser radiation
into the optical fiber. This often requires first fabricating a
point with a particular taper on the end of the fiber and then
making the lens usually by a melting procedure. A reliable
procedure for reproducibly making a point with a given taper at the
end of an optical fiber is highly desirable.
SUMMARY OF THE INVENTION
The invention is a procedure for etching a tapered point on a
cylindrically symmetric body in which a liquid layer is located on
top of the etchant. In a preferred embodiment, the cylindrically
symmetric body is made of glass which contains silicon dioxide.
Typically, the glass body is an optical fiber used in a
communication system in which the etchant is hydrofluoric acid and
the glass fiber contains at least 80 weight percent silicon
dioxide. The liquid in the liquid layer is less dense than the
etchant so that it floats on the etchant. The liquid in the liquid
layer should not be miscible with the etchant or chemically react
with the etchant. Typically, various oils are used such as
sunflower seed oil, mineral oil, 80W90 gear oil, etc. Use of such a
liquid yields tapered points on optical fibers that are highly
reproducible. Also, the liquid layer prevents escape of fumes from
the etchant so that a hooded or vented operation is not
required.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a typical optical fiber with coating partially removed
and the end partially etched;
FIG. 2 shows a typical apparatus for the practice of the invention
including etchant, container, liquid layer and means to monitor
etching process; and
FIG. 3 shows a series of views of an optical fiber being etched in
accordance with the invention.
DETAILED DESCRIPTION
The invention involves an etching procedure for fabricating tapered
points on roughly cylindrically symmetric bodies. The invention is
based on the discovery that use of an inert liquid layer above the
etchant is highly advantageous. It produces cleanly tapered points
without producing any etching above the taper. The process is
highly reproducible. The liquid layer also prevents fumes from the
etchant from escaping into the atmosphere.
In general, the invention is applicable to a large number of
situations where an etchant is used to shape a particular body. It
is most often used to shape cylindrically symmetric
structures--typically a tapered point--in a variety of substances
that can be etched by a chemical etching agent. A particular
important use of such a tapered point in optical fibers is to make
small lenses by melt-back for coupling light from sources to fiber
or from fiber to detector.
Although the process has largely been directed toward glass fibers
for communication use, the invention is applicable to a large
variety of materials. In particular, it is applicable to any
material that can be chemically etched such as glass, metals
(including alloys), crystals (including polycrystalline materials),
plastics, etc.
Various etchants may be used in the practice of the invention.
Generally, the etchant should etch the material being etched at a
reasonable rate and the etch should etch approximately
isotropically (although rotation of the material around the
cylindrical axis might increase the isotropic nature of the
process). Generally, a smooth etch (one that does not produce pits)
is the most useful, naturally. Typical etchants are aqueous HF for
titanium, and various glasses including quartz glass and aqueous
sodium perchlorate for copper.
The nature of the liquid used in the liquid layer is also of
importance in the practice of the invention. Generally, the liquid
should not be miscible in the etching solution. Naturally, some
miscibility is permitted provided a separate layer of liquid
remains above the etchant. Generally, miscibility should be less
than about 20 volume percent.
Also, the density of the liquid in the liquid layer should be less
than the density of the etchant so that the liquid layer floats on
the etchant. Generally, the etchant is an aqueous solution with
density near 1 gm/cc. Thus, the liquid in the liquid layer should
have a density less than 1 gm/cc. Mixtures of liquids (either
miscible in one another or not) may be used to adjust properties
such as density and adherence to the material being etched.
The liquid in the liquid layer should also be chemically inert to
the etchant. A limited amount of chemical attack is tolerable, but
excessive attack should be avoided. Also, low vapor pressure is
preferred to avoid evaporation of the liquid and to prevent the
escape of fumes.
Typical liquids that are useful as liquid layers are sunflower seed
oil, mineral oil, 10-40 or 20-50 motor oil, heavy gear oil (80W90),
various synthetic motor oils, castor oil, corn oil, linseed oil,
whale oil, Neat's foot oil, etc.
Generally, the taper obtained in etching points in materials like
glass have an angle of about 28 degrees. Limited experiments seem
to indicate that the taper angle does not depend on the liquid in
the liquid layer. The angle of the taper is most easily changed by
slowly moving the body being etched either up or down depending on
whether a narrower or wider taper is desired.
A preferred embodiment of the invention is the fabrication of small
lenses at the ends of optical fibers by first etching a point on
the fiber and then melting the point to form the lens. Typically,
the optical fiber (often called quartz fiber) is made mostly of
silicon dioxide with small amounts of germanium and phosphorus (and
often other materials) present to adjust index of refraction,
glassiness, etc. The fiber is usually made of at least 90 weight
percent silicon dioxide, often more than 95 weight percent.
Experiments were carried out on a typical fiber cable (a single
mode optical cable quartz fiber) with outside diameter of 125
.mu.m. About 100 .mu.m of this diameter is outside organic coating
which is removed in hot (about 110 degrees C.) concentrated
sulfuric acid.
The fiber is conveniently etched using a rather concentrated
solution of hydrofluoric acid (generally between 35 weight percent
and about 100 weight percent but usually the standard HF solution
of about 49 weight percent).
The etching operation is carried out by inserting the exposed
quartz fiber into the etching solution which is covered with a
liquid layer (generally sunflower seed oil). A typical side view of
the optical cable 10 in the process of being etched is shown in
FIG. 1. The organic coating 11 has been removed from the end of the
cable, exposing the quartz fiber. The end of the quartz fiber has
been partially etched and the level of the etching solution 14 is
near the end of the taper. Continued etching produces a tapered
point.
FIG. 2 shows a typical apparatus 20 with container 21 filled with
etchant 22 and liquid layer 23. Immersed in the etchant 22 and
liquid layer 23 is a cylindrical body 24 (generally a glass fiber)
to be etched into the form of a tapered point. Also shown is a
microscope for observing the etching process.
FIG. 3 shows various stages in the etching process. FIG. 3a shows
the fiber when initially immersed in the etchant and liquid layer
(labeled oil). Gradually, the fiber is etched as shown in FIG. 3b
and the contact of fiber with etchant gradually drops down.
Continued etching produces an etched taper as shown in FIG. 3c. The
etching process is completed as the etchant drops away from the
fiber as shown in FIG. 3d. Repetition of the same process produces
tapers of the same shape and geometry. The process is automatic in
that when the point is formed and the etchant-liquid interface
breaks away from the quartz, all etching stops.
Often, in the case of optical fibers, the tapered point is further
processed to fabricate a lens on the end of the optical fiber to
improve coupling between laser source and optical fiber or between
optical fiber and detector. The lens is usually formed by melting
back the tapered point using a source of heat such as an electric
arc. A particular advantage of the etching process is that the
reproducibility of the tapered point so that the lens forming
process produces lenses of identical properties.
* * * * *